This application claims the priority of foreign application No. 197 12 916.1 filed in Germany on Mar. 27, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a supporting disk for a supporting disk bearing of an open-end spinning rotor comprising a damping, essentially cylindrical running surface defined by encircling border edges, which running surface comprises a helically shaped groove having a beginning and an end.
The U.S. Pat. No. 5,551,226 teaches that in the case of the known supporting disk of this type, the beginning and end of the helically shaped groove are located on the border edges which define the running surface. As during operation, the open-end spinning rotor exerts its greatest load on the border edges, the danger exists that the edges of the damping running surface, which is made of plastic, will crumble as a result of the interruptions on the surface caused by the groove.
German published patent application 33 42 768 teaches a similar supporting disk, in which the helically shaped groove has only one thread. The groove extends to both border edges, so that here also the same danger as in the above mentioned prior art exists.
One purpose of both known helically shaped grooves is to prevent the running surfaces heating up excessively during operation thus preventing that in the center of the running surface heat damage which could destroy the running surface.
It is an object of the present invention to eliminate the risk of the supporting disks of the above mentioned type crumbling at the border edges.
This object has been achieved in accordance with the present invention in that the beginning and the end of the helical groove are provided with an eased runout, which is located at a distance from the respective border edge.
The beginning and end of the groove are thus still located according to the present invention on the cylindrical running surface, whereby at both points the groove gradates over from the groove base into the running surface. The helically shaped groove thus does not extend to the extremely loaded border edges, so that damage of the running surface, in the form of crumbling, is prevented at these points.
For this purpose, the two eased runouts are located diametrically opposed to one another. Thus imbalances, which could be caused by the gradation of the helically shaped groove into the running surface, are avoided.
The groove is advantageously provided with two and a half helical turns. This is a good compromise between two loads which are not compatible, namely operational temperature and surface pressure. From experience, it is known that, with a higher number of thread turns, the heat build-up of the running surface is reduced. On the other hand, the stress bearing area of the running surface is reduced by the number of thread turns, which results in a higher surface pressure by the open-end rotor.
In order that the whole width of the running surface can be used to a large extent, it is further provided that the distance of the eased runouts from the respective border edges measures approximately 1 mm.